Isothermal crystallization of poly(vinylidene fluoride) blended with the ionic liquid [Emim]2[Co(SCN)4]: Simultaneous analysis of crystalline phases by infrared spectroscopy and differential scanning calorimetry
Luís Amaro Martins, José Luís Gómez Ribelles, Carlos M. Costa, Daniela M. Correia, S. Lanceros‐Méndez, Ivan Krakowsky, Isabel Tort-Ausina
Abstract
The combination of poly (vinylidene fluoride) (PVDF) with ionic liquids (ILs) is increasingly being studied for the development of smart materials. Together with the functional response provided by the IL, its incorporation into PVDF allows to nucleate specific electroactive phases of the polymer, depending on the processing conditions. Thus, the isothermal crystallization of PVDF incorporating different contents of the magnetic ionic liquid bis(1-ethyl-3-methylimidazolium) tetrathiocyanatocobaltate ([Emim]2 [Co(SCN)4]) is reported in this work. Morphological properties of the films were obtained by field emission scanning electronic microscopy (FESEM), and particularly, for the higher contents of IL, segregation was observed through artifacts present on the film surface. This fact has been further confirmed by energy-dispersive x-ray spectroscopy (EDX). The growth of the crystalline phases of PVDF during isothermal crystallization at different temperatures has been analyzed by Fourier transform infrared (FTIR) spectroscopy. Although α, β and γ crystalline phases were present in all samples, their relative percentages varied greatly with the amount of IL present, demonstrating that [Emim]2 [Co(SCN)4] is a strong inductor of the electroactive (EA) phases of PVDF. By evaluating both FTIR and DSC data, this effect has been ascribed to the higher melting temperatures of the EA structures whose formation is favored at higher crystallization temperatures. The melting temperature (Tm) of the β phase is higher than that of the α phase, whereas Tm for the γ phase is higher than for α and β phases. Thus, together with the specific functional properties provided by the IL, such as magnetic response and ionic conductivity, the addition of [Emim]2 [Co(SCN)4] strongly influences PVDF's crystallization kinetics, proving to be a simple and very effective way to nucleate specific phases of PVDF, according also to the specific processing conditions.